This invention relates in general to antifriction bearings and, more particularly, to a method of measuring preload in a multirow bearing assembly.
In its most basic form a two row bearing assembly has an inner component and an outer component, one of which rotates relative to the other about an axis of rotation, and in addition, rolling elements arranged in two rows between the inner and outer components. The rolling elements roll along raceways on the inner and outer components, and while all of the raceways are inclined, the raceways for the one row are inclined in a direction opposite the raceways for the other row. This enables the bearing assembly to transfer thrust loads in both axial directions. Furthermore, when one of the raceways in the bearing assembly is capable of being adjusted axially, the setting for the bearing assembly may be adjusted to one of end play or preload, depending on the position of the adjusted raceway. When end play exists, the bearing assembly possesses a limited amount of axial and radial clearance between the inner and outer components, whereas in preload no clearance exists, and the rolling elements are continuously loaded.
The wheels on automotive vehicles to a large extent revolve on two row bearing assemblies, and this holds particularly true as to those wheels that are independently suspended. Two row bearing assemblies are traditionally supplied to automotive companies set to a condition of end play, but with the capacity to be adjusted. The automotive companies make the final adjustments, and often this is one of slight preload, particularly where the two rows of rolling elements are close together. However, some bearing assemblies are now being supplied fully unitized and preset. That type of bearing assembly contains at least one initially separate race, and that race is initially configured to impart end play to the bearing assembly. Using measurements taken from the bearing assembly after it is partially assembled and from the initially separate race, the end front face of that initially separate race is ground down to provide the bearing assembly with the desired amount of preload once the race is installed in the assembly. Thereafter, the assembly is unitized to permanently capture the initially separate race and the two rows of rolling elements within the assembly. After the bearing assembly is unitized, the preload should be checked to insure that it falls within acceptable tolerances. After all, too much preload will cause early failure of the bearing assembly and retard rotation. On the other hand, excessive end play will concentrate the radial load at only a few rollers and may produce wheel shake or reduce bearing life.
To be sure, procedures exist for at least estimating preload in unitized two row bearing assemblies. Perhaps the easiest amounts to nothing more than measuring the torque in the bearing assembly, that is, the resistance to rotation that resides in the bearing assembly itself. But torque provides only an approximation of preload and is distorted by lubrication and by seals which are also captured in such bearing assemblies. A more sophisticated procedure involves subjecting the bearing assembly to thrust loads in both axial directions and plotting those loads against deflection. From the plot one can determine preload. See Keller, Computerized Bearing Measurements Optimize Machine Output, Design News, Jun. 4, 1984. This procedure consumes considerable time, and while it works quite satisfactory in a laboratory environment, it is not suitable for use in a production line.
The present invention resides in a method of ascertaining preload in a first bearing assembly having multiple rows of rolling elements organized to transfer thrust loads in both axial directions. The method requires comparing the deflection characteristics of the first bearing assembly with the deflection characteristics of a second bearing assembly set to a condition of end play. The invention also resides in a method of ascertaining the amount of end play in the second bearing.